1. Field of the Invention
The invention relates to semiconductor wafer processing systems and, more particularly, the invention relates to a method of improving plasma processing performance.
2. Background of the Invention
As structures fabricated upon semiconductor wafers become smaller and the wafers become larger, there are many factors that contribute to non-optimal processing of the wafers. To improve processing throughput of wafers (e.g., increase the number of wafers processed within a unit of time), it is desirable to, for example, further increase the etch rate, decrease the chamber cleaning frequency, decrease chamber cleaning duration. Furthermore, any improvements to the process results, such as improvements in electron shading, improved photoresist selectivity, decreased photoresist striations, residue control, chamber cleanliness, aspect ratio dependent etching, substantially reduced charging damage, mitigating notching, improved profile control, improved etch stop, decreased microloading, mitigation of gap fill difficulties and the like, are desirable.
As an example of a desired improvement, as structures fabricated upon semiconductor wafers are reduced in feature size, residue control during aluminum etching has become a serious issue. Some aluminum films generally contain a small amount of copper, i.e., 0.5 to 2 percent, which can result in residue formation that can interfere with further processing that is required to complete an integrated circuit. During an aluminum etch process, the aluminum etch rate and by-product removal rate is much faster than those of copper. Therefore, copper residues are easily formed especially in an aluminum alloy where copper segregation typically occurs. The residues form in the copper rich areas of the aluminum alloy. The mechanism for producing copper-induced residue is the following: copper in the aluminum-copper alloy is harder to etch and is not necessarily evenly distributed throughout the alloy. Local concentrations of copper are harder to etch and sacrifice etch rate, resist selectivity, and profile control. Such non-uniform etching results in some regions of the final etched product becoming raised regions with respect to surrounding regions. Such raised regions are referred to as xe2x80x9cresiduexe2x80x9d. The residue may not have any copper in it at all but was the result of the copper in the aluminum.
The wafer can be heated to higher temperatures to enhance copper etch by-product removal as well as the removal of more volatile by-products. However, for temperatures above approximately 130xc2x0 C., the photoresist will reticulate, and even for small temperature rises above the optimal for process control, process factors are difficult to control, for example, the aluminum stack profile. Another conventional method of addressing this issue is to increase the ion bombardment of the wafer. However, additional ion bombardment occurs at the expense of resist selectivity and profile microloading.
Therefore, a need exists in the art for a method of generally improving processing of semiconductor wafers, an example of which is reducing copper-induced residue produced during aluminum etching.
The disadvantages associated with the prior art are overcome by the present invention of a method for reducing plasma process related effects that impact both wafer processing and the structures produced by the process. The method comprises the steps of plasma processing a semiconductor wafer and exposing the semiconductor wafer or the plasma to photons to facilitate improvement of the process.